Use of clinoptilolite for the removal of nickel ions from water: Kinetics and thermodynamics

This paper describes the removal of Ni(II) ions from aqueous solutions using clinoptilolite. The effect of clinoptilolite level, contact time, and pH were determined. Different isotherms were also obtained using concentrations of Ni(II) ions ranging from 0.1 to 100 mg L−1. The ion-exchange process follows second-order reaction kinetics and follows the Langmuir isotherm. The paper discusses thermodynamic parameters, including changes in Gibbs free energy, entropy, and enthalpy, for the ion-exchange of Ni(II) on clinoptilolite, and revealed that the ion-exchange process was spontaneous and exothermic under natural conditions. The maximum removal efficiency obtained was 93.6% at pH 7 and with a 45 min contact time (for 25 mg L−1 initial concentration and a 15 g L−1 solid-to-liquid ratio).